1. Technical Field
Exemplary embodiments of the present invention relate to an optical device, and more particularly, to an optic modulator.
2. Related Art
Recently, with the increase in signal processing speed of integrated circuits, much research has been conducted on a method for implementing communications between semiconductor chips using optical signals. A core element of an optical integrated circuit for processing such optical signals is an electro-optic modulator. The electro-optic modulator generates an optical signal by modulating a constant intensity of light emitted from an external internal light source.
The optic modulator within the optical integrated circuit performs a function of converting an electrical signal into an optical signal. In order to perform such a function, the optic modulator uses an electro-optic effect. In particular, a semiconductor material such as silicon may have an effective refractive index which changes due to an internal carrier concentration changed by an external electric field. When such a plasma-dispersion effect is used to modulate a refractive index of a partial region of the optic modulator into an electrical signal, the optic modulator having a unique structure may generate an optical signal through an interference effect with light incident on the optic modulator. As a method for changing the internal carrier concentration of the optic modulator, a P-I-N diode structure is mainly used. The optic modulator having a P-I-N diode structure includes an intrinsic semiconductor region and an extrinsic semiconductor region. The intrinsic semiconductor region is set to a region through which light passes. Then, an external electrical signal is applied through the extrinsic semiconductor region being in contact with the intrinsic semiconductor region and doped with a dopant, and carriers are supplied to or discharged from the intrinsic semiconductor region, thereby modulating the effective refractive index of the corresponding region.
FIG. 1 is a cross-sectional view of an optic modulator having a P-I-N diode structure.
The optic modulator 100 having a P-I-N diode structure includes an intrinsic semiconductor region 132 through which light passes and N-type and P-type doping regions 131 and 133 for supplying/discharging carriers to/from the intrinsic semiconductor region 132. A passivation layer 140 is formed over the intrinsic semiconductor region 132, the N-type doping region 131, and the P-type doping region 133. Through the passivation layer 140, plugs 151 are connected to the N-type doping region 131 and the P-type doping region 133, respectively. Pads 161 are formed over the respective plugs 151.
The optic modulator having a P-I-N diode structure has the following problems.
The volume of the intrinsic semiconductor region 132 is relatively large, and the contact area between the intrinsic semiconductor region 132 and the N-type and P-type doping regions 131 and 132 is relatively small. Thus, it takes a long time to supply/discharge carriers.
Furthermore, the switching type of the P-I-N diode structure is limited. In particular, it takes a long time to discharge minority carriers supplied to the intrinsic semiconductor region 132, because the minority carriers have a long life time.